1. Field of the Invention
The present invention relates to direct injected internal combustion engines using gaseous fuels.
2. Description of the Related Art
The term "direct injected" refers to the use of fuel injectors for injecting fuel directly into the combustion chambers of internal combustion engines. The term "gaseous fuel" is defined herein as referring to both compressed gas fuel such as compressed natural gas (CNG) or hydrogen (H.sub.2) and liquefied gas fuels such as liquefied petroleum gas (LPG).
There are numerous potential advantages in using gaseous fuels in engines in place of the more commonly used liquid fuels. For example, it is well appreciated that the undesirable exhaust emissions from an engine using a gaseous fuel can be lower than for a comparable engine using liquid fuel. Further, at the present time, the use of certain gaseous fuels can translate to a significant cost saving for the user due to the per liter cost thereof as compared to the per liter cost of the commonly used liquid fuels.
The applicant has developed certain spark ignited, direct injection two stroke and four stroke cycle internal combustion engine technologies which primarily use liquid fuel. It would however be advantageous to also have a system which can inject gaseous fuel directly into the combustion chambers of the engine as this may lead to a simpler system requiring less mechanical components as well as preferably facilitating more accurate metering control of the gaseous fuel to the engine as compared with prior art systems.
Although diesel engines generally use direct injection fuel systems and certain diesel engines which use gaseous fuels are known, the operating environment within which these fuel systems must operate are significantly different to those encountered within a spark ignition engine. For example, modern spark ignition engines typically operate at significantly higher engine speeds than for corresponding diesel engines. This therefore provides a more demanding environment for a direct injection fuel system and the control system therefor when used in a spark ignition engine.
Furthermore, reasonably accurate control of the fuel distribution within the combustion chamber is required in a spark ignition engine to ensure that there is a combustible mixture present immediately adjacent the spark plug at the appropriate time during each engine operating cycle. In the compression ignition operation of a diesel engine, such accurate fuel distribution control is not as critical.
It is therefore an object of the present invention to provide a system for the direct injection of gaseous fuel into a spark ignited internal combustion engine.
It is also an object of the present invention to provide a method of controlling a gaseous fuel direct injection system for a spark ignited internal combustion engine.